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Crossley D.1, Hinderer J.2 and Riccardi U.3

 

The measurement of surface gravity


Reports on Progress in Physics Vol. 76 N°4 (2013) (47pp)
doi:10.1088/0034-4885/76/4/046101
 
1 Department of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Blvd., St Louis
MO 63108, USA.
2 Ecole et Observatoire des Sciences de la Terre, University of Strasbourg, CNRS, France.
3 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse (DiSTAR) Università‘Federico II di Napoli, L.go S Marcellino 10, 80138 Naples, Italy.
 

Abstract
Fig ROPThis review covers basic theory and techniques behind the use of ground-based gravimetry at the Earth’s surface. The orientation is toward modern instrumentation, data processing and interpretation for observing surface, land-based, time-variable changes to the geopotential.
The instrumentation side is covered in some detail, with specifications and performance of the most widely used models of the three main types: the absolute gravimeters (FG5, A10 from Micro-g LaCoste), superconducting gravimeters (OSG, iGrav from GWR instruments), and the new generation of spring instruments (Micro-g LaCoste gPhone, Scintrex CG5 and Burris ZLS). A wide range of applications is covered, with selected examples from tides and ocean
loading, atmospheric effects on gravity, local and global hydrology, seismology and normal modes, long period and tectonics, volcanology, exploration gravimetry, and some examples of gravimetry connected to fundamental physics. We show that there are only a modest number of very large signals, i.e. hundreds of μGal (10−8 ms−2), that are easy to see with all gravimeters (e.g. tides, volcanic eruptions, large earthquakes, seasonal hydrology). The
majority of signals of interest are in the range 0.1–5.0μGal and occur at a wide range of time scales (minutes to years) and spatial extent (a few meters to global). Here the competing effects require a careful combination of different gravimeter types and measurement strategies to efficiently characterize and distinguish the signals. Gravimeters are sophisticated
instruments, with substantial up-front costs, and they place demands on the operators to maximize the results. Nevertheless their performance characteristics such as drift and precision have improved dramatically in recent years, and their data recording ability and ruggedness have seen similar advances. Many subtle signals are now routinely connected with known geophysical effects such as coseismic earthquake displacements, post-glacial rebound, local hydrological mass balances, and detection of non-steric sea level